Effect of timing of a calcium salt supplement containing palmitic and oleic acids on production responses of early lactation dairy cows

Fifty-six multiparous cows were used in a randomized complete block design experiment and assigned to either a control diet containing no supplemental fat (CON) or a diet supplemented with calcium salts (CS) of palmitic (C16:0) and oleic (C18:1) acids (FAT) either from calving to 24 DIM (fresh period, FR) or from 25 to 67 DIM (peak period, PK). Fresh diets contained (% DM) 17% CP, 23% forage NDF, and 25% starch. Peak diets contained (% DM) 17% CP, 19% forage NDF, and 28% starch. The CS contained 60% C16:0 and 30% C18:1 (total fatty acid basis) and was added at 1.90% of diet DM replacing soyhulls in CON diets. The statistical model included the random effect of block and cow within block and treatment, and the fixed effect of treatment, time, and their interactions. Results are presented in the sequence CON vs. FAT. During FR there was no effect of treatment on DMI (21.2 vs. 21.5 kg/d, P = 0.25), milk yield (40.6 vs. 39.1 kg/d, P = 0.30), or BW change (−2.59 vs. −2.20 kg/d, P = 0.35). Compared with CON, FAT increased milk fat content (4.62 vs. 4.95%, P = 0.02) and yield (1.80 vs. 1.96 kg/d, P = 0.02) and ECM (45.6 vs. 48.4 kg/d, P = 0.05). During PK there was no effect of treatment on DMI (28.1 vs. 28.3 kg/d, P = 0.73), or BW change (0.39 vs. 0.30 kg/d, P = 0.38). Compared with CON, FAT increased milk yield (51.5 vs. 54.0 kg/d, P = 0.05), milk fat content (3.52% vs. 3.63, P = 0.05) and yield (1.82 vs. 2.02 kg/d, P < 0.01) and ECM (51.5 vs. 55.2 kg/d, P < 0.01). A treatment by time interaction was observed for DMI during PK (P = 0.05) because intake was higher for FAT compared with CON after wk 5 of calving. We observed that cows that received FAT compared with CON during FR increased milk yield by 2.7 kg/d (P = 0.04) and ECM by 2.9 kg/d (P = 0.03) during PK indicating a positive carryover effect of CS supplementation early postpartum. Our results demonstrate that feeding a CS supplement containing 60% C16:0 and 30% C18:1 during early lactation increases milk fat yield and ECM without changes in DMI or BW during the fresh and peak periods.